$ sudo apt-get update
W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://extras.ubuntu.com maverick Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/maverick/Release
W: Some index files failed to download, they have been ignored, or old ones used instead.

How can I remove these warnings? Running apt-get update has given me these warnings from the beginning of my fresh 10.10 install.